docs: def _get_hypocentral_depth_term(self, C, rup):
          """
          Returns the hypocentral depth scaling term defined in equations 21 - 23
          """
          if rup.hypo_depth <= 7.0:
              fhyp_h = 0.0
          elif rup.hypo_depth > 20.0:
              fhyp_h = 13.0
          else:
              fhyp_h = rup.hypo_depth - 7.0
  
          if rup.mag <= 5.5:
              fhyp_m = C["c17"]
          elif rup.mag > 6.5:
              fhyp_m = C["c18"]
          else:
              fhyp_m = C["c17"] + ((C["c18"] - C["c17"]) * (rup.mag - 5.5))
          return fhyp_h * fhyp_m